1. Field of the Invention
This invention relates to apparatus for treating an elongate cord, such as the type incorporated into power transmission belts and, more particularly, to an oven for heating the cord so as to effect curing of a processing substance applied thereto.
2. Background Art
It is known to use load carrying cords in all types of power transmission belts, i.e. V-belts, V-ribbed belts, toothed belts, etc., and particularly those used in industrial applications. Typically, the cords are made from fiber material, such as polyester fiber, aramid fiber, glass fiber, and the like. To improve adhesion with the belt rubber, it is known to pre-treat the fiber cords. For example, it is known to treat the cords with resorcinol-formalin-latex (RFL) alone or to use the RFL treatment after pre-treating the cords with an epoxy or isocyanate compound. It is also known to adhere rubber gum after the RFL treatment.
Apparatus are known for continuously pulling a cord from a supply under a fixed tension, using a drive roller, and to guide the cord in a predetermined path for processing. In this predetermined path, the cord moves through an adhesive processing liquid in a first dip tank, after which the cord is directed into an oven in which it is exposed to heated air. The cord continues to move to outside of the oven to complete a first treatment step. Additional dip tanks and ovens may be used to sequentially apply different processing liquids, followed by heating, which takes place once or any desired number of times following processing liquid application during the process. In addition to using different processing liquids, different heating temperatures can be used in the ovens. Additionally, the cords may be drawn to different tensions to produce optimal properties for the cord as a belt component. Upon completion of the treatment of the cord, the cord can be continuously collected on a take-up reel.
An exemplary prior art oven for use in the above type of system is disclosed in Japanese Unexamined Patent Publication No. H.4-146232. Through intake and discharge fans, hot air is supplied to and discharged from a heating chamber. The heated air is circulated within the heating chambers. This unit is characterized as a "vertical" type unit.
It is also known to circulate the air in a partially closed system outside of the heating chamber. Through separate fans, some air is controllably drawn into a circulating air stream in a conduit communicating between intake and discharge openings on the oven and exhausted therefrom. As the heated air is circulated, the concentration of combustible gases produced within the heating chamber from vaporization of processing solvent such as toluene, or the like, is diminished.
In conventional apparatus for treating a cord, to effect high efficiency heat treatment, it has been generally necessary to advance the cord in a predetermined path at a relatively high speed. With this arrangement, the cord with the processing liquid thereon may be advanced through the heating chamber in the oven and out against a guide roller without the processing liquid being fully hardened. As a result, some of the processing liquid may adhere to and accumulate on the surface of the guide structure, which may be a roller, or the like. This condition may ultimately be aggravated to the point that the operation of the system is impaired.
To promote drying, it is also known to raise the temperature in the oven. However, cords generally have optimum treating temperatures. Thus, it is not practical to increase the temperature in the ovens without adversely affecting the properties of some cords.
As an alternative to raising the temperature in the oven, it is known to increase the size of the oven so that the cord travels for more extended periods therewithin. This results in the overall size of the apparatus increasing, which may add to the equipment cost and increase operating costs by reason of more extensive heat loss. Additionally, more installation and operating space is required. Further, it may be more difficult to perform regular inspections of, and maintenance on, the apparatus and to re-thread the cord as when the type of cord to be processed is changed. In a worst case, safety may be compromised by this construction.